Hair roller heater

ABSTRACT

For controlling the heating of heating posts in a hair roller heater in which each heating post includes a respective resistive heating element, an emulator or physical model has a thermal time constant that is about equal to the time constant of each post assembly to emulate the thermal behaviour of the heating posts during both heating and cooling. Direct temperature feedback from the emulator to a thermostatic switch is used for controlling the current delivered to the heating elements. The emulator includes a pair of insulators between which a heating element is provided, one of the insulators being thermally coupled to a conductive mounting to which the posts are directly connected

TECHNICAL FIELD

The present invention relates to an electrical heater for hair curling rollers, more especially to a heater having resistance elements for heating each roller.

BACKGROUND OF THE INVENTION

A hair roller heater generally comprises a heated base on which metal posts are provided for receiving hair curling rollers, and a housing enclosing the base, posts and rollers to reduce heat loss. In use, hair is wound about each heated roller, which is typically held in place by a clip while the rollers cool.

In electrical resistance hair roller heaters each post may enclose a heating element and this permits an equal amount of heat to be supplied to each post and good heat transfer, predominantly by conduction, from the post to the roller surrounding it. There are number of demands placed upon a hair roller heater of this type. It must be reliable in operation and safe (not producing dangerously high temperatures on exposed heating posts), the hair roller heater should preferably be a lightweight unit, and of course manufacturing costs should be minimized. For best performance and convenience, each roller should be efficiently heated to the desired temperature of around 90-120° C. in a short period of time.

As in all electric heating units, the roller heater must be provided with temperature controlling means, such as a thermostatic switch, in order not to overheat the rollers. To avoid a stimulus-response lag, the temperature sensor and heating posts should be co-located, however, this presents some practical difficulties. Due to the size of the heating posts and the thermostatic switch and the necessity to place the rollers over the posts, the conventional thermostatic switch cannot be placed in internal or external contact with the heating posts. In the past, therefore, the thermostatic switch has typically been placed adjacent the base of the heating posts. This produces a significant stimulus-response lag, and although this is satisfactory for the lower heating rates which have conventionally been used, it is problematic where a much higher heating rate is desired to reduce heating times. It is an object of the present invention to overcome or substantially ameliorate the above disadvantages or more generally to provide an improved electrical heater for hair curling rollers.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided an electrical resistance heater for a set of hair rollers comprising:

a plurality of post heating elements electrically connected in series;

a circuit connecting the post heating elements for receiving power from a power supply;

a plurality of post assemblies, each post assembly having an outer surface of a shape complementary to an inner surface of a hair roller, each post assembly enclosing one of the post heating elements, each post assembly having a thermal time constant in heating and cooling;

an emulator heating element connected in the circuit in series with the post heating elements;

an emulator body thermally coupled to the emulator heating element for emulating the thermal response of each post assembly, and

a thermostatic switch co-located with and thermally coupled to the emulator body, the thermostatic switch being connected in series with the post heating elements.

In another aspect of the invention there is provided an electrical resistance heater for a set of hair rollers comprising:

a housing having a floor, at least one upper opening and a closure for closing each upper opening, wherein the housing is made from insulating material or is thermally insulated;

a mounting member having an inner side facing the floor and an opposing outer side;

a plurality of posts disposed on the mounting member to project from the outer side, each post having an outer surface of a shape complementary to an inner surface of a hair roller, each post including a post heating element for heating each post, each post having a thermal time constant in heating and cooling;

an emulator body mounted to the inner side of the mounting member;

an emulator heating element thermally coupled to the emulator body, the emulator body having a time constant that is about equal to the thermal time constant of each post;

a circuit connecting the post heating elements and emulator heating element for receiving power from a power supply, and

a thermostatic switch thermally coupled to the emulator body, the thermostatic switch being connected in series in between the power supply and the post heating elements.

Preferably the metal mounting member is planar and spans between side walls of the housing. Alternatively the mounting member may be curved in one or two dimensions, or formed in an alternative shape.

Preferably each post comprises a hollow cylindrical metal skin with a closed end and an opposing open end, the open being mechanically fixed to, or integral with, the mounting member, each post heating element is generally cylindrical and helically wound and is received coaxially within the post and wherein a cylindrical dielectric liner extends about an inner side of the each post to separate the post and post heating element.

Preferably the emulator body comprises first and second sheets of insulating material between which the emulator heating element is received, wherein the first sheet is secured to the inner side of the mounting member and the second sheet is secured to the thermostatic switch. Preferably the first and second sheets of insulating material are planar sheets of mica and the post heating elements and emulator heating element are connected in series with the thermostatic switch.

In still another aspect the invention provides a process for controlling the heating of heating posts in a hair roller heater in which each heating post includes a respective resistive heating element, comprising the steps of: emulating the thermal behaviour of the heating posts during both heating and cooling, and using temperature feedback from the emulation for controlling the current delivered to the heating elements.

Preferably the heating elements are electrically connected to a power supply in series with a thermostatic switch for controlling the heating of the heating posts, and the emulating step is performed using a physical model of the heating post that is proportional to heating post temperature and the temperature feedback is provided by thermally coupling the model and the thermostatic switch.

This invention provides an electrical resistance heater for a set of hair rollers which is effective and efficient in operational use, which may be economically constructed and which allows the temperature of heating posts to be accurately controlled at high heating rates.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a vertical section longitudinally through a hair roller heater according to a preferred embodiment of the invention;

FIG. 2 is a schematic vertical section of a heating post of the heater of FIG. 1;

FIG. 3 is a vertical section through a hair roller of the heater of FIG. 1;

FIG. 4 is an exploded view of the temperature emulator of the heater of FIG. 1, and

FIG. 5 is transverse section through the heater of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the hair roller heater of the invention includes a housing 10 assembled from upper and lower shells 11, 12 joined together circumferentially. The lower shell 12 has a floor 13 in which a downwardly opening recess 14 is provided. The upper shell 12 defines an upper wall 15 of the housing in which circular apertures 16 are arrayed, aligned concentrically with upright axes 17. A concave closure 18 sealingly engages about the periphery of the top shell 11 to form a closed volume 19 at the top of the housing 10. The housing 10 and closure 18 are preferably moulded from a polymer which is an insulator having reasonable stability at elevated temperatures, such as polypropylene.

Intermediate the floor 13 and the upper wall 15 an aluminum mounting sheet 20 is fixed to the housing 10 and extends generally horizontally between its side walls. The mounting sheet 20 has an inner side 21 facing the floor 13 and an opposing outer side 22.

A plurality of posts 23 are fixed to the mounting sheet 20 to project from the outer side 22 coaxially with the axes 17. Each post 23 has a cylindrical aluminum skin with a closed end 24 uppermost and an opposing open end 25 received in close contact with an opening in the mounting sheet 20, with the peripheral edge of the post 23 swaged over to fix it to the mounting sheet 20. The closed end 24 is aligned with the upper wall 15 to substantially protect users from the hot posts 23.

A helically wound post heating element 35 is generally axially extending, being received coaxially within the post 23. The element 35 is sandwiched between outer and inner dielectric liners 25, 26. The outer dielectric liner 25 abuts the inner wall of the post 23 to separate the post 23 and post heating element 35. The inner dielectric liner 26 is supported on an internal wire frame 27. The wires 28 electrically connecting the post heating elements 23 in series pass through respective apertures in a plug 29 of insulating material which otherwise closes the open ends 25 of each post 23.

The apparatus further includes a plurality of rollers 30 including a tubular body 31 made of aluminum with an cylindrical inner surface 32 complementary to the outer face of the posts 23. An insulating grip 34 is fixed to one end of the tubular body 31.

A physical model or emulator 40 copies or emulates the temperature versus time of one of the posts 23 when it receives a roller 30 for heating. The temperature measured by emulator 40 thereby provides a feedback of the post temperature. Thus, this temperature feedback can be direct to the sensor or thermostatic switch 41, without requiring means to directly measure the post temperature in the interior of the roller 30. The thermostatic switch 41 includes a bimetallic element. The emulator body comprises a stack of four mica sheets 42-45 of like rectangular dimensions with apertures 50 at opposing ends thereof for receiving a fastener (not shown). A first sheet 43 has a central section 46 with opposing parallel edges offset inwardly of the outer end portions to provide a waisted form. An emulator heating element 47 is wound around the central section 46 with the ends 48, 49 of the element extending from longitudinally opposing ends of the central section 46. A second sheet 42 is mounted between the emulator heating element 47 and the mounting sheet 20 on an inner side of the emulator, while third and fourth adjacent sheets 44, 45 are provides on the outer side of the emulator 40. The first sheet 42 is secured directly to the inner side 21 of the mounting member 20. The thermostatic switch 41 is secured and directly thermally coupled to a central position on the outer side of the fourth sheet 45. The post heating elements 24 and emulator heating element 44 are connected in series with the thermostatic switch 41, a temperature-sensing safety switch 50 and an on/off switch 46.

In use, the rollers 30 are entered over the posts 23 through the apertures 16, before the closure 18 is put in place. The plug 45 is connected to mains supply and the switch 46 operated to supply current to the heating elements 35, 44. The temperature on the outer wall of the post 23 is emulated by the emulator 40. In the embodiment shown the emulator 40 provides the same temperature as the external temperature of the post 23, however alternatively some temperature proportionality may be used. The temperature initially reaches 118° C. in approximately 200 seconds. At this temperature of approximately 118° C. the thermostatic switch 41 opens to cut power to the elements 35, 44. The emulator 40 and posts 23 then begin cooling at approximately the same rate, before the lower limit of the thermostatic switch 41 is reached and the thermostatic switch is closed. A temperature-indicating lamp (not shown) controlled by the thermostatic switch 41 may be illuminated (or extinguished) to indicate to the user that the rollers 30 may be used. By co-locating the thermostatic switch and the emulator body between the mounting sheet 20 and the lower shell a conventional, low-cost bimetallic thermostatic switch may be used for controlling the post heating elements at a high heating rate without significant stimulus-response lag.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof. 

1. An electrical resistance heater for a set of hair rollers, comprising: a housing having a floor, at least one upper opening, and a closure for closing each upper opening, wherein the housing is an insulating material or is thermally insulated; a mounting member having an inner side facing the floor and an opposing outer side; a plurality of posts disposed on the mounting member and projecting from the outer side, each post having an outer surface with a shape complementary to an inner surface of a hair roller, each post including a post heating element for heating each post, and each post having a thermal time constant in heating and cooling; an emulator body mounted to the inner side of the mounting member; an emulator heating element thermally coupled to the emulator body, the emulator body having a time constant that is substantially equal to the thermal time constant of each post; a circuit connecting the post heating elements and emulator heating element for receiving power from a power supply; and a thermostatic switch thermally coupled to the emulator body, the thermostatic switch being connected in series between the power supply and the post heating elements.
 2. The heater of claim 1 wherein each post comprises a hollow cylindrical metal skin with a closed end and an opposing open end, the open end is mechanically fixed to, or integral with, the mounting member, and each post heating element is generally cylindrical and helically wound and is received coaxially within the posts and including a cylindrical dielectric liner extending about an inner side of each post, separating the post from this post heating element.
 3. The heater of claim 1 wherein the emulator body comprises first, seconds and third sheets of insulating material, the emulator heating element is wound around the second sheet, the second sheet is received between the first and third sheets, and the first sheet is secured to the inner side of the mounting member.
 4. The heater of claim 3 wherein the first and second sheets are mica sheets, and the post heating elements and the emulator heating element are electrically connected in series with the thermostatic switch.
 5. An electrical resistance heater for a set of hair rollers comprising: a plurality of post heating elements electrically connected in series; a circuit connecting the post heating elements for receiving power from a power supply; a plurality of post assemblies, each post assembly having an outer surface with a shape complementary to an inner surface of a hair roller, each post assembly enclosing one of the post heating elements, and each post assembly having a thermal time constant in heating and cooling; an emulator heating element connected in the circuit in series with the post heating elements; an emulator body thermally coupled to the emulator heating element for emulating thermal response of each post assembly,; and a thermostatic switch co-located with and thermally coupled to the emulator body, the thermostatic switch being connected in series with the post heating elements.
 6. A process for controlling heating of heating posts in a hair roller heater in which each heating post includes a respective resistive heating element, comprising: emulating thermal behaviour of the heating posts during both heating and cooling, and, using temperature feedback from the emulation, controlling the current delivered to the heating elements.
 7. The process of claim 6 wherein the heating elements are electrically connected to a power supply in series with a thermostatic switch for controlling the heating of the heating posts, the emulating is performed using a physical model of the heating post and providing a temperature that is proportional to heating post temperature when the heating post receives a hair roller, and the temperature feedback is provided by thermally coupling the model and the thermostatic switch. 